<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box1 {
      display: flex;
      /* justify-content: flex-start; */
      /* justify-content: flex-end; */
      /* justify-content: center; */
      /* justify-content: space-between; */
      /* justify-content: space-around; */
      /* justify-content: space-evenly; */
      /* align-items: flex-start; */
      /* align-items: flex-end; */
      /* align-items: center; */
      width: 600px;
      height: 600px;
      background-color: pink;
      /* align-items: baseline; */

      /* 不设置子元素的高，将自动拉升至父元素高度 */
      align-items: stretch;
    }
    .box1 div {
      width: 100px;
      /* height: 100px; */
      border: 1px solid #333;
      box-sizing: border-box;
    }
  </style>
</head>
<body>
  <div class="box1">
    <div><h1>flex</h1></div>
    <div><h5>flex</h5></div>
    <div><h3>flex</h3></div>
    <div><h2>flex</h2></div>
  </div>
  <div class="box2">2</div>
  <div class="box3">3</div>
</body>
</html>